iterator

问题 I am curious what the fastest way to consume an iterator would be, and the most Pythonic way. For example, say that I want to create an iterator with the map builtin that accumulates something as a side-effect. I don't actually care about the result of the map , just the side effect, so I want to blow through the iteration with as little overhead or boilerplate as possible. Something like: my_set = set() my_map = map(lambda x, y: my_set.add((x, y)), my_x, my_y) In this example, I just want to

问题 ArrayList 's list iterator does implement the remove method, however, I get the following exception thrown: UnsupportedOperationException at java.util.AbstractList.remove(AbstractList.java:144) By this code: protected void removeZeroLengthStringsFrom(List<String> stringList) { ListIterator<String> iter = stringList.listIterator(); String s; while (iter.hasNext()) { s = iter.next(); if (s.length() == 0) { iter.remove(); } } } What am I missing here? I have verified that the List<String> I am

问题 ArrayList 's list iterator does implement the remove method, however, I get the following exception thrown: UnsupportedOperationException at java.util.AbstractList.remove(AbstractList.java:144) By this code: protected void removeZeroLengthStringsFrom(List<String> stringList) { ListIterator<String> iter = stringList.listIterator(); String s; while (iter.hasNext()) { s = iter.next(); if (s.length() == 0) { iter.remove(); } } } What am I missing here? I have verified that the List<String> I am

问题 ArrayList 's list iterator does implement the remove method, however, I get the following exception thrown: UnsupportedOperationException at java.util.AbstractList.remove(AbstractList.java:144) By this code: protected void removeZeroLengthStringsFrom(List<String> stringList) { ListIterator<String> iter = stringList.listIterator(); String s; while (iter.hasNext()) { s = iter.next(); if (s.length() == 0) { iter.remove(); } } } What am I missing here? I have verified that the List<String> I am

问题 I am using scala Iterator for waiting loop in synchronized block: anObject.synchronized { if (Try(anObject.foo()).isFailure) { Iterator.continually { anObject.wait() Try(anObject.foo()) }.dropWhile(_.isFailure).next() } anObject.notifyAll() } Is it acceptable to use Iterator with concurrency and multithreading? If not, why? And then what to use and how? There are some details, if it matters. anObject is a mutable queue. And there are multiple producers and consumers to the queue. So the block

问题 To my surprise this Concept-like assertion fails in RangeV3. #include<vector> #include<range/v3/algorithm/copy.hpp> int main(){ static_assert(ranges::WeaklyIncrementable<std::back_insert_iterator<std::vector<double> >>()); } Why is that? This, among other things means that I cannot use the ranges::copy algorithm as I use to do with std::copy . std::vector<double> w(100); std::vector<double> v; ranges::copy( begin(w), end(w), std:back_inserter(v) ); // compilation error, concept not fulfilled.

问题 I have a problem that I want to solve with itertools.imap(). However, after I imported itertools in IDLE shell and called itertools.imap(), the IDLE shell told me that itertools doesn't have attribute imap. What's going wrong? >>> import itertools >>> dir(itertools) ['__doc__', '__loader__', '__name__', '__package__', '__spec__', '_grouper', '_tee', '_tee_dataobject', 'accumulate', 'chain', 'combinations', 'combinations_with_replacement', 'compress', 'count', 'cycle', 'dropwhile',

问题 Having a ParseObject object how can I loop through its fields and get the name of the field along with the value of it? This would really help me minimize my code. 回答1: Hmm, ParseObject contains key-value pairs, and I think you can't iterate though it. But. I found something called .keySet() method of ParseObject. It returns ... well, the set of keys (excluding createdAt, updatedAt, authData, or objectId). I think you can convert it into an array and iterate trhough it? Something like this:

问题 I want to list all possible ways to concatenate a list of strings, example: Input: strings = ['hat','bag','cab'] Output: concatenated = ['hatbag','hatcab','hatbagcab','hatcabbag','baghat','bagcab', 'baghatcab','bagcabhat','cabhat','cabbag','cabhatbag','cabbaghat'] I've tried using for loops for this simple 3 string list, but I can't figure out how to do it with many strings in the list. Can someone please help? 回答1: This is a great case for the itertools module. You're looking for

问题 I need to collect an iterator over a slice of &str s into a collection of &str s. The problem is that the iterator yields &&str s. I tried to map from &word to word , and while it works, I don't know if it is considered good or if there are better options available. The problem: use std::collections::HashSet; fn main() { let words = &["hello", "world", "I'm", "a", "Rustacean!"]; let hashset = words.iter().collect::<HashSet<&str>>(); } Playground error[E0277]: a collection of type `std: